1. Field of the Invention
The invention relates to a portable vibratory screed machine, and, more particularly, relates to a portable vibratory screed machine having a vibration restraint configured to reduce undesirable vibrational wear on and extend the life of the machine's engine.
2. Discussion of the Related Art
Numerous screed machines employ vibratory action to tamp and smooth concrete in the strike off step of a concrete finishing operation. Known vibratory screed machines comprise, for instance, an elongated blade extending horizontally and transversally at lower ends of a pair of handles adapted to be hand held and operated for displacing the wet screed over a concrete surface. A motor is provided above the blade and between the handles. The motor's output extends to the blade, where it is connected to a vibratory assembly having one or more eccentric weights configured to impart vibrations to the screed blade upon motor operation. A handle permits an easy and constant correction of the level of the concrete with minimum effort. A throttle control is provided at the handle such that the speed of the motor may be adjusted as the blade is displaced over the concrete being surfaced.
One specific example of a known vibrating plate machine is disclosed in U.S. Pat. No. 4,340,351, which describes a vibratory concrete screed used in the final finishing of concrete. This screed requires two operators. As another example, U.S. Pat. No. 4,641,995 describes a vibratory concrete screed, which rides on forms to screed narrow strips of concrete, such as walks. This screed is mounted on the operator via a complicated harness counter-weighted frame and is powered by electricity. As a result, the screed requires electrical power, and the screed requires manipulation of lengthy extension cords. These and other screeds are designed to be used only after concrete has been leveled and preliminarily tamped. None of these screeds is suitable to “wet screed” large slabs of freshly poured concrete that has not yet been leveled or tamped at all.
In the absence of widely accepted wet screeding machines, the industry standard for wet screeding is to perform that process manually. Typically, in manual wet screeding, a 2-inch by 4-inch board that is 8-foot to 20-foot long is manipulated manually by one or two men hand working in conjunction with as many as four laborers, known as “puddlers,” who push the fresh concrete in place with concrete rakes. The hand puddling and wet screeding process is slow, inefficient, labor intensive, and extremely fatiguing, particularly if large slabs are poured and finished over the course of an entire day or more. It is also often requires the addition of more water to the concrete mix to make it more workable. The addition of water to produce slumps of 6-inch to 8-inces is common in the industry to increase the workability of the concrete, allowing the finisher to effectively hand “wet screed” the fresh concrete. The hand process typically limits the finisher to the average pour of 6,000 to a maximum of 8,000 square feed of slab per day for crew of six. The additional water reduces the strength of the concrete, causing voids and weak spots in the cured concrete.
Proposals have been made to reduce the labor required for wet screeding by providing portable vibratory “wet screed” machines. These machines typically have an engine coupled to an drive shaft. The engine is generally an internal combustion engine having a housing, a fuel tank, a clutch housing, etc. The drive shaft is configured to drive a vibrator drive shaft of the vibratory assembly. The engine housing or a support therefore is secured to a housing for the vibrator drive shaft at one point by a clamp. The clamp location is approximately midway between a centroid of the engine and the blade. The clamp provides only limited restraint to the engine and drive shaft relative to the vibratory assembly along the x-y reference plane. Vibrations generated upon screed operation by the eccentric vibratory assembly therefore are transmitted to the clamp point and generate severe vibrations on the engine about all three (x, y, z) axes. The vibrations are known to cause failures not only in the clutch housing, but also of the handle assembly, the fuel tank, oil seals, the engine block, etc. Engine block failures are the most problematic because the engine is by far the most expensive component of the wet screed. The screed therefore is typically considered spent when the engine block fails. Vibratory wet screeds therefore historically have had a reputation of being unreliable, hindering their acceptance by the industry as a whole.
In light of the foregoing, a portable vibratory screed machine is desired with reduced undesirable vibration on the motor and extended motor life associated with operation of the vibratory screed machine in the surfacing of concrete.